Questions about the halving

I'm not super knowledgeable about crypto and how it's value is derived. But from what I understand, the halving reduces the amount of bitcoin you can receive for X amount of time mining.

If this is the case, does this devalue mining companies since they will have their income essentially cut in half? Or is there more to it than that. Obviously the current stock of crypto they already have mined will become more valuable, hence the big run up last year, but their future output is slashed. Is this right?